Comparison of Alkali-Activated Regolith Simulants: Commercial Formulations and Etna Volcanic Ashes for Lunar Construction

COMPARISON OF ALKALI-ACTIVATED REGOLITH SIMULANTS: COMMERCIAL FORMULATIONS AND ETNA VOLCANIC ASHES FOR LUNAR CONSTRUCTION F. Santoro de Vico1*, A. Driouich1,2, G. Melchiori1, M. Massironi1,2, L. Valentini1,2 1 Center of Studies and Activities for Space “G. Colombo”, University of Padova, Via Venezia 15, 35131 Padova ([email protected]) 2 Department of Geosciences, University of Padova, Via Gradenigo 6, 35131 Padova. Introduction: As space agencies plan lunar settlements, balancing construction challenges with sustainability is crucial. This research optimizes alkali-activated lunar regolith formulations for In Situ Resource Utilization (ISRU), based on both a commercial simulant and locally sourced materials. The need for sustainable construction materials that can be produced on-site is of paramount importance for reducing payload mass and enabling long-term lunar habitation. Alkali-activated materials represent a promising solution since they do not require the transport of an additional binder such as Portland cement. Methods: We initially implemented a Design of Experiments (DoE) approach on commercial simulant formulations, studying key parameters such as alkaline activator amount, metakaolin addition, and curing temperature. With this commercial simulant we explored three different alkaline activators (NaOH, and sodium silicate) and investigated urea as an additive to modify rheological properties and enhance mechanical performance. This optimization phase allowed us to identify the most promising formulations based on compressive strength, workability. Experimental procedures included mechanical testing, rheological measurements, and microstructural characterization to understand reaction mechanisms. Identification of Italian Simulants: Following this optimization phase, we conducted a systematic investigation to identify potential lunar simulant sources within Italy, particularly from Mount Etna, using XRD and XRF analyses. These were evaluated against NASA simulant requirements, identifying materials analogous to Apollo 14 samples. The mineralogical and chemical composition of selected Etna basalts showed remarkable similarities to lunar regolith, particularly in terms of silica content, aluminum oxide, and iron oxide percentages. Results: The results demonstrated that sodium silicate-based activators provided superior mechanical properties, while urea effectively improved workability without significant strength reduction. We applied our optimized formulations to Italian simulants, developing Alkali-activated binders specifically tailored to lunar regolith characteristics. Comparative testing between commercial and Italian simulants revealed distinct advantages of the Etna-derived materials, including improved workability, and comparable mechanical strength. Benefits and Applications: This alkaline activation approach offers significant advantages for lunar ISRU: minimal Earth-transported materials, and potential radiation shielding properties. Additional benefits include compatibility with 3D printing technologies and excellent dimensional stability, which are crucial for structural applications in the harsh lunar environment. Conclusion: This sequential approach, first optimizing with commercial simulants and then applying to Italian simulants from Etna, advances our understanding of alkali-activated materials for lunar construction, paving the way for sustainable and efficient lunar settlements. Our findings demonstrate that locally-sourced simulants can match and potentially exceed the performance of commercial alternatives, offering a pathway to more sustainable research in space construction materials. Acknowledgement: This study was carried out within the Space It Up project funded by the Italian Space Agency, ASI, and the Ministry of University and Research, MUR, under contract n. 2024-5-E.0 - CUP n. I53D24000060005. Also we want to thank GLAMS (Geopolymers for Lunar Additive Manufacturing and Sensing) project, funded by the Italian Space Agency (ASI) grant Research Days 2023-6-U.0 F93C23000200005.